Thrombosis of the Caudal Aorta

Thrombosis of the Caudal Aorta or the Iliac arteries is the thrombus formation in arteries of the limbs that can cause blood supply interruption.

Specific locations for these thrombi are the caudal aorta, iliac arteries, femoral artery in the hindlimb, and very rarely the brachial artery in the front limb. Circulatory problems in the muscles (and later in all tissues) can cause pain, resulting in lameness.

Etiology

The etiology of Thrombosis of the Caudal Aorta has been described as being caused by the migrating larva of Strongylus vulgaris.

Clinical Signs

This lameness is specific in that it occurs after or during work, is sudden in onset, and can be very severe (grade 3 to 5 of 5), but can diminish or disappear within minutes to hours after ceasing work. Because of the severe pain, horses may sweat, show anxiety, and be very restless, which can make the condition look like azoturia or even equine colic.

Diagnosis

Blood chemistry and a clinical work-up for colic are negative. Clinical examination shows lower perfusion in the affected limb, lower temperature (thermography can be useful in these cases), and absence or lower pressure of arterial pulse. On the non-affected limb, the veins can show clearly while they are indistinct on the affected limb. Ultrasonography can show lower blood flow in the blood vessels of the affected limb (using Doppler). With transrectal ultrasonography it is sometimes possible to find the thrombus and measure its size, but with a rectal examination one can determine the decrease or absence of arterial pulse or fremitus in the iliac arteries.

Treatment

Treatment is focused on medication: anticoagulants (Heparin 100 IU/kg sc SID, aspirin 5 to 10 mg/kg po SID, Phenprocoumon 0.08 to 0.16 mg/kg IV initial bolus, gradually reduced), Nonsteroidal anti inflammatory drugs, and antimicrobial drugs (Metronidazole 25 mg/kg PO BID and thiabendazole 4g/45 kg PO once weekly for 3 weeks or Ivermectin or Moxydectin) to act against Strongylus vulgaris larvae when they are expected to be the cause.

Successful surgical removal of the thrombus has been performed with a thrombectomy catheter, but this requires that the exact location of the thrombus be determined by ultrasonography or scintigraphy.

Prognosis

Prognosis for thrombosis of the aorta and the iliac arteries is guarded, especially when the underlying cause is not known.